The present invention relates to the treatment or prevention of coccidiosis in bovine animals that are susceptible to coccidia infection.
Coccidiosis is an intestinal disease that affects several animal species. The disease, however, represents a particularly important problem in the raising of poultry and cattle.
In cattle, coccidiosis is primarily a disease of the young where there is crowding, stress, and/or nonimmune animals. Older cows act as a reservoir and shed oocysts into the environment. Shipping, weaning, dietary changes, and steroid therapy can precipitate coccidiosis. Even cattle immune to their own endemic species of coccidia can become ill when exposed to different species. Coccidiosis may result in death.
The causative agent is a protozoan that has the ability to rapidly multiply. Damage is incurred by the rapid multiplication of the parasite in, and the subsequent rupture of, cells of the intestinal lining. Several species of coccidia occur in cattle but Eimeria zuemii and Eimeria bovis are the most frequently isolated species associated with the disease.
Bovine coccidia undergo various stages of development. Infection gives rise to a microscopic egg (called an oocyst), which is passed out in manure. Under proper conditions, the oocyst develops within three to seven days to form a sporulate oocyst, which is capable of infecting other cattle. The sporulated oocyst contains eight bodies (called sporozoites), each of which is capable of entering a cell in the animal""s intestine. When sporozoites enter intestinal cells, they divide several times, and each resulting offspring is capable of entering another intestinal cell. Male and female cells are produced. The male fertilizes the female to produce an oocyst, which in turn ruptures the intestinal cell and is passed in the manure. Thousands of oocysts may be passed in the manure of an infected animal.
Oocysts are resistant to environmental stresses and contaminate feed and water, infecting other animals. Ingestion of oocysts may not produce disease, since animals can carry them without being affected. Recovered animals develop immunity and are partially resistant to reinfection.
Several anticoccidial drugs are available for treatment or prevention of coccidiosis, including sulfonamides such as sulfaquinoxaline and sulfamethazine, amprolium, lasalocid decoquinate, and monensin. Drugs that are useful to treat coccidiosis are not necessarily useful to prevent the disease.
Drugs currently used for treatment or prevention of coccidiosis suffer from certain disadvantages. For example, monensin, a polyether ionophore that is administered in feed is sufficiently toxic that it must be gradually administered. Amprolium requires a complicated dosing regime.
Antibiotics have been employed to treat various infections in bovine cattle. For example, macrolide antibiotics are frequently administered to cattle at risk of developing respiratory infections upon arrival at a feedyard. Such antibiotics are advantageous in that they persist at high levels in blood and tissue, often achieving the desired preventive or therapeutic effect with only a single dose.
According to the present invention, macrolide antibiotics have been determined to be effective in the treatment or prevention of coccidiosis in bovine animals. The macrolide antibiotics are effective, for example, when administered prior to development of coccidiosis, at the time that such animals enter a feed lot and are exposed to stresses that may otherwise induce the disease.
That the antibiotics would be effective, e.g., in preventing coccidiosis in animals exposed to, or infected with, coccidia was not predictable. As noted above, the ability to prevent coccidiosis is not normally predictable even for agents known to treat the disease. Also, the mechanism by which the macrolide antibiotics might be found effective against Eimeria was not known.
The present invention relates to a method of treating or preventing coccidiosis in a bovine animal comprising administering to the mammal an effective amount of a macrolide antibiotic. Administration to prevent the disease is preferred. The antibiotic is preferably of the azalide class.